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mchandler

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Posts: 2
Reply with quote  #1 

Hey guys, long time lurker, first time poster.  I have been researching the heck out of these solar air heaters and have come up with an idea of something i would like to try and am looking for some feedback.

The easiest way to describe is just by looking at the pictures, but here's a few hi/lo lights:

I am using tempered glass for the top (glazing i think it's called) - thinking it would give the best results.

In areas where the bottom is covered by 3 layers of screen, i would use reflective bottom - ran across a post on here somewhere i think that with a 3 layer screen it was a bit better with a reflective bottom.  In the area where the air comes in (inlet), it's a single screen layer to bottom and that would be matte black.

the airflow is really only going THROUGH 2 screens, however I have a single screen across the entire top, that no air would typically be passing through but just be able to pull in more heat without restricting the airflow anymore than a double layer.

I'm going to use aluminum screen ( I am pretty sure ), because it seems to be most efficient, however I have not seen a consensus on black or charcoal screen being better - I'm guessing whichever one is more matte??

There was 2 versions of the design that I had.  One was kind of pointed at the top - like a rocket, while the other was rectangle but installed DIAGONALLY.  in this way, all sides would be pointing up and the hottest air would be at the highest point inside the box.

The size of the box is based on my ability to get a tempered glass insert for a screen door from lowes.

Insulation would be all around the box and bottom and that hot temperature tolerant TUFF-R i think...

I'm really just in the design phases and getting a lot of inspiration from you all. I would really love any input / advice as to what is no good and what might work.

Thanks,
Matt
Joppa, MD

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netttech

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Posts: 720
Reply with quote  #2 
Welcome MC,

First, I have charcoal aluminum screen, that I lightly spray painted black. If you angle the screen or can it will lightly paint the screen. I believe it would make a difference in the color, being black. I think someone has experimented with color & may post their results.

I like the pyramid top design, since it should ensure all hot air goes out & isn't trapped. You mentioned using 'glass', can it be easily cut to that shape?? Is the glass cheaper than other forms of glazing, plexiglass, twin-wall or TUFR (I think that's correct), poly-bicarbonate??

Building to the size of materials available (or on-hand) is always a good idea.

I think someone mentioned that glass can be coated with a sustance to trap heat 'in' & if the wrong side is outward, it would degrade the light entering the panel. Hopefully, someone that knows for sure will post on glass usage.

I didn't see any mention whether this is passive or active (with a fan). If it's active, how big a fan are you planning?

If you're intending the panel to be passive...how big is your vent holes? Passive means it's a naturaal flow of heated air, don't restrict it by having too small of vent holes.

It looks like a good 1st project! Keep us posted & include pictures if possible. [smile]

Jeff
Central IL
Seatec

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Posts: 219
Reply with quote  #3 
I tried a piece of glass from my patio door, I pane and it blocked too many watts from the sun, so I did not use it, I may try turning it around to see if there is any difference. Glass is very heavy and cost a lot to replace if it gets broken.

Wayne
Garage_Hermit

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Posts: 2,240
Reply with quote  #4 
I always understood that it is impossible to cut tempered glass...

I guess this kind-of confirms it...

http://www.diynot.com/forums/viewtopic.php?t=18791

Still, that is only an inconvenience - no doubt a workaround can be found...
(such as using a rectangular pane, and using metal inserts or artificial glass / acrylate sheet etc. for any triangular elements...).

G_H


__________________
(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
Silverback

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Posts: 174
Reply with quote  #5 
Seatec - Aside from the screen, making the back wall a matte-black would capture a little more heat. Given that you have 3 layers of screen, not that much light will make it to the back wall, but once it's there the thin foil of the insulation will transfer it to the back layer of screen. No need to chance reflecting it out of the box. If you look at the pictures of the box construction here I built a 3 layer box like yours, but with a different air flow configuration. The screen is charcoal, painted matte-black also.(You should ignore most of the maddness in the other pics.)

I like the aesthetics of the angled top, but suspect most people here will recommend building as large as possible and to design an efficient intake/outtake vent geometry to remove the hot air. There are plenty of great examples on this site.

Have fun and post results once it's up and running.


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Silverback CT
solardan1959

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Posts: 1,845
Reply with quote  #6 
Matt,
   Got to carry on and agree with everyone here, The first design is nice but nut practical with the glass panel. I not sure about how the second crooked panel would look.  I am not sure the benefit would be there since you still doing the screen like a normal upright panel.  But you did get me thinking of a diamond shape again.  Three layers of aluminum screen will probably not catch enough light, when I used three layers and Mylar behind it I still can barely see it but people have used three layers of aluminum and you can clearly see the writing on the foil panel.  (meaning two much light is returning)
   Don't let us discourage you, just think about what is being said and how it may work for you.
Dan
mchandler

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Posts: 2
Reply with quote  #7 

A little background:  I have a 2 story custom house currently under construction - 3400sf.  The roof faces South / Southwest and is in a WIDE open field.  I am trying to super-insulate everything.  All exterior walls are 2x6 and I believe R23, attic is R60.  I plan on mounting this on the roof, however it is REALLY quite high so I am hoping to have it really sturdy and solid for lowest possible maintenance.  I plan on testing this on the ground before putting on the roof.

@Seatec:  So I never really thought about any kind of additional additive or glazing that would prevent heat. That would really stink had I built this whole thing without that in mind.  Is there any way to tell?  Would the glazing be visible or noticeable?  I'm guessing the specs from manufacture that come with the product would tell me as well?


@netttech:  It's going to be an active box (meaning a fan of some sort)...

I'm also concerned about having 2 HUGE 6 inch holes in the roof.  I am a little more ok having smaller in/out lets - maybe 3-4inches and a little more resistance - although I guess I could be convinced otherwise.  I'm guessing you can get 6inch rubber boots like you can for 2-3 inches coming out of the roof? Sort of like those used for waste water drain vents??

@Silverback:  I kept going back and fourth between an angled top and installed diagonally.  The downside of rectangle box installed diagonally is asthetics - would look like it was done wrong.  The upside as far as I was thinking was airflow and perhaps if we get any heavy snows, no flat surfaces on the high up roof for that snow to sit all day / or multi days.

As for the screen color:  Lowe's Hardware around my area sells charcoal and black aluminum screen.  Is there any reason you bought charcoal and painted black?  I was really leaning to purchasing the screen and using out of the box to minimize and paint smell and whatnot.

@SolarDan1959:  Yeah, I hadn't really thought through the glass shape other than keeping it rectangle (no cutting) and having the extra glass overhang...also performance wise, is there any benefit of tempered glass over a regular glass?

KevinH

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Posts: 560
Reply with quote  #8 
There seems to be quite a bit of variation in the standard window screen available from different sources, both in the wire diameter and size and shape of the opening.  I checked some fiberglass screen I have from a few years ago and the openings are bigger than on my window screens.  There are also differences in the aluminum screen I have.  Some has a square opening and some has a more rectangular opening.

The zero pass concept is meant to pass the air parallel to and between the screen layers keeping it away from both the glazing and the back.  It is still an experimental concept and we don't know yet if it will make a significant difference in performance.  In your design the angled screen would likely disrupt the zero pass flow.  It would still probably generate just as much heat as other screen-based designs.  Having one of the three layers parallel to the glazing is an interesting idea.

As for tilting the whole collector, that might help some with the problem of some areas getting less air flow and getting hotter.  There is still a straight shot from top to bottom corners, but with the top sides angled the hot air should rise and mix better with the flow.  One disadvantage is that if the collector is mounted on the house it does not blend in with the windows and other horizontal/vertical lines on the house.  Predicting air flow is difficult.  It doesn't always do what you want or expect.  Some people have tried doing smoke tests or thermal images to get an idea of what is really happening.  That requires a way to easily remove the glazing and a design that allows making changes that affect the flow.

It sounds like you have been studying and learning from what others have done which is good.  If this is your first collector, however, don't get caught in the trap of over analyzing the design and missing part or all of a heating season (like I did).  Build something.  Each build will be a learning experience that makes the next build better and easier.

Kevin H
MN
Garage_Hermit

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Posts: 2,240
Reply with quote  #9 
Matt, thanks a lot for the background, it helps:

Quote:
I have a 2 story custom house currently under construction - 3400sf.  The roof faces South / Southwest and is in a WIDE open field.  I am trying to super-insulate everything.  All exterior walls are 2x6 and I believe R23, attic is R60.  I plan on mounting this on the roof, however it is REALLY quite high so I am hoping to have it really sturdy and solid for lowest possible maintenance.  I plan on testing this on the ground before putting on the roof.


It's your project, but if I were building a new house, there is *no way* I would put a collector on the roof! Any collector, period.

I'd use the roof itself as a solar collector!
In fact, that's just what I'm doing today:
15.5°C day today, no sun (10/10s stratus at 600 feet)
It's a gray day: local airport weather
http://www.itimeteo.com/observations/metar/LFRT.html

(mine is somewhat better, 3 miles inland & microclimate due to being on estuary rather than coast...) http://france.lachainemeteo.com/meteo-france/ville/previsions-meteo-plerin-4079-0.php
Got 21.3°C in the lounge, 23 in the kitchen window, 22 in the mezzanine.
I am sucking air out of the roof at 22°C

That is much warmer than the outside air, and is higher than my house temp, so I am warming the house for free, with one 30-watt fan and occasional ceiling fan (100 Watts)

Translated into real talk, that means, house is at 70°F, and it is a 59°F sunless day.

All due to the power of... ROOF SLATE !

Maybe you should think about your roof, before U get too far along with your build !

Best regards, and a big welcome to the site !

Garage Hermit

P.S.

I should be surprised if your builder would even guarantee the works, particularly if he does not do them himself...

Also, what does your Architect think ? And your Thermal Design Bureau ?
Not to mention the Government's Inspector ?


__________________
(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
joebehr

Registered:
Posts: 109
Reply with quote  #10 
If you still have not decided on a roof system or a specific material check out this option...

http://activeroof.info/active-roof-faq.php

joebehr
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